1. Field of the Invention
The present invention relates generally to electronic chip cooling devices and more particularly to a device which will provide active cooling to reduce temperature excursions of electronic chips, which will limit thermal fatigue, increase product life cycle, allow for larger chips and permit chips to be directly attached to substrates with unmatched coefficients of thermal expansion with less reliability concerns.
2. Discussion of the Prior Art
In today's high power PC's and workstations, the number of on/off cycles is limited due to fatigue in the solder interconnections and device wiring because of the high operating temperature of the chip as a result of the high power dissipation. Conventional passive cooling is limited since it relies on a temperature difference between the chip and ambient which is cooled by a fan. Thus, the operating temperature is high, resulting in large temperature excursions between the on and off states. As a consequence of these large temperature excursions that the chips are subjected to, the size of the chip is limited to allow for the required on/off cycles.
In the more recent environmental PC's, power management techniques are being used to conserve power by monitoring system activity and reducing power levels in parts of the system. Thermal cycling is potentially a major concern, since each inactive mode will allow time for the chip to cool. The typical cycling of an environmental PC is represented by curve 1 in FIG. 1, where the normal operating temperature is arbitrarily indicated as 80.degree. C. and the temperature during a sleep cycle is reduced to 70.degree. C. Curve 1 shows that the cycling of such a machine will have a frequency of the order of a few seconds as opposed to the frequency of a normal on/off cycle which is typically one day. Assuming a two second cycle time, on average, this translates to about 15,000 cycles per 8 hour day, with a 10.degree. C. swing. This compares to a total specification of 20,000 on/off cycles for the lifetime of a machine (with a temperature swing of 50.degree. C.). These "mini" cycles can add up to 4 million cycles a year and can pose a serious reliability problem.
Thus, there is a need for a method or structure that can limit either the number of thermal cycles and/or the temperature swings to enhance the product reliability.